FT-IR interferogram signal processing for uniform-time sampling

A new approach to Fourier transform-infrared (FT-IR) signal acquisition and processing has been developed recently. This approach relies on digital signal processing (DSP) and enables the use of sigma-delta analog-to-digital converters (ADCs). Data are simultaneously oversampled from both the infrared (IR) and reference laser channels at uniform time intervals. This approach contrasts sharply with the traditional method, in which reference channel zero-crossings are used to trigger ADC sampling of the IR channel at equal increments of optical path difference (OPD). In one embodiment of the new approach, data from the laser channel are processed to values of mirror position. These position data then can be used to interpolate the IR signal. The uniform time sampling method shifts instrument complexity from hardware to software, while improving the spectral accuracy by fully correcting the effects of optical velocity variation. The correction is sufficient even with a sinusoidal variation in the optical retardation rate. This study demonstrates the approach using the Lomb-Scargle periodogram.